It is well known that vane compressors, which are employed as vacuum pumps and the like, are equipped with a rotor that undergoes eccentric rotation within a cylinder (a stator), and vanes that are slidably pressed against the inner peripheral surface of the cylinder or the outer peripheral surface of the rotor by spring force. In association with rotation of the rotor, a stroke to draw a fluid into compression chambers partitioned by the vanes, and a stroke to compress and discharge the drawn-in fluid, are repeated. In a case in which it is desired to enhance the compression performance of vane compressors, typical practice is to link the vane compressors in a multistage arrangement in their axial direction, so as to obtain a high-compression ratio fluid from the vane compressor of the final stage.
In Patent Document 1, there is proposed a multistage rotary compressor of vane design in an attempt at a concentric multistage arrangement. In the multistage rotary compressor disclosed therein, a cylindrical post is arranged in concentric fashion in the interior of a housing, and an orbiting ring rotates eccentrically between the circular inner peripheral surface of the housing and the circular outer peripheral surface of the post. A pair of vanes pressed by spring force against the circular inner peripheral surface of the orbiting ring are attached to the post situated towards the center, and a pair of vanes pressed by spring force against the circular outer peripheral surface of the orbiting ring are attached to the housing situated towards the outside. Through eccentric rotation of the orbiting ring, a fluid is repeatedly compressed through the agency of compression chambers formed to the outer peripheral side and the inner peripheral side thereof.